Trunk Problems

For some reason I am unable to open my trunk with the key fob or side panel.  The only way is with the actual key into the hole.  Any ideas why this happens?  Is there a way to "reset" the trunk mechanism? 

Also, the damned trunk brake light lens fell out... they can never get this right!

Thanks for any feedback.

2004 CLK500

do not lock it with mechanical key. just close it. it will lock from centralized pushbutton.

try again.

thanks for the reply, but no such luck   any other ideas?